Quantitative description of residual gas distribution in strong-heterogeneity tight sandstone gas reservoirs and potential tapping strategies : A case study of the old area of northern Su 11 Block in the Sulige Gas Field

After more than ten years of development in the old area of northern Su 11 Block in the Sulige Gas Field, some problems get more and more prominent, such as the increase of low-yield and low-pressure gas wells, uneven production of reserves, and complex distribution of remaining gas. In order to improve its development effect, it is required to accurately describe the distribution of remaining gas between wells and between layers by means of the fine characterization technology for complex fluvial sandstone reservoirs and the geological modeling-numerical simulation integrated remaining gas evaluation technology, after investigating the development experience of similar gas reservoirs. Then, after the technical boundaries of layers and well selections in sidetracking horizontal wells, sidetracking wells and layer-adjusting wells are defined, specific potential tapping strategies are formulated to guide the on-site potential tapping operation in this block. And the following research results were obtained. First, the fine characterization technology for complex fluvial sandstone reservoirs can realize the fine characterization in the level of single sandbody, quantitatively describe dominant reservoirs and provide model guidance for geological research of fluvial reservoirs. Second, the remaining gas reserve evaluation technology based on the dynamic analysis method and numerical simulation method accurately describes the lateral and vertical distribution characteristics of the remaining gas, and points out the direction of potential tapping in the next step. Third, the distribution of the remaining gas reserves in the old area of northern Su 11 Block can be divided into three modes, including uncontrolled well pattern types, intralayer heterogeneity types and interlayer heterogeneity types. For the uncontrolled well pattern type, priority is given to a sidetracking horizontal well for potential tapping. For the intralayer heterogeneity type, priority is given to a sidetracking well. And for the interlayer heterogeneity type, priority is given to a layer-adjusting well. Fourth, the technical boundaries of wells and layer selections in a sidetracking horizontal wells, sidetracking wells and layer-adjusting wells are determined. In the old area of northern Su 11 Block, 5 sidetracking horizontal wells, 8 sidetracking wells and 79 layer-adjusting wells have been deployed in total. Fifth, up to now, the efficiency of on-site measure wells is up to 100% and the cumulative natural gas increment is 1.01×108 m3. In conclusion, the potential tapping countermeasures for the old areas of tight sandstone gas reservoirs proposed on the basis of the research results achieve remarkable results in natural gas production increase and are worth popularizing and using for reference. © 2020, Natural Gas Industry Journal Agency. All right reserved.